Technical Field
This disclosure relates to precision metrology, and more particularly to machine vision inspection systems and other optical systems in which a variable focal length lens may be utilized to periodically modulate a focus position.
Description of the Related Art
Precision machine vision inspection systems (or “vision systems” for short) may be used for precise measurements of objects and to inspect other object characteristics. Such systems may include a computer, camera, optical system, and a stage that moves to allow workpiece traversal. One exemplary system, characterized as a general-purpose “off-line” precision vision system, is the QUICK VISION® series of PC-based vision systems and QVPAK® software available from Mitutoyo America Corporation (MAC), located in Aurora, Ill. The features and operation of the QUICK VISION® series of vision systems and the QVPAK® software are generally described, for example, in the QVPAK 3D CNC Vision Measuring Machine User's Guide, published January 2003, which is hereby incorporated by reference in its entirety. This type of system uses a microscope-type optical system and moves the stage to provide inspection images of small or large workpieces at various magnifications.
In various applications, it is desirable to perform high speed measurements for high throughput in either stationary or non-stop moving inspection systems. With respect to Z-height measurements, conventional machine vision inspection systems may utilize various types of operations (e.g., points-from-focus operations, etc.) which require movement of the camera through a range of Z-height positions. In confocal systems, movement may similarly be required through a range of Z-height positions (e.g., to determine a position that results in maximum confocal brightness, etc.). In such systems, the speed at which the Z-height measurements can be performed may be limited by the motion of one or more physical components of the systems through the range of Z-height positions. There is a need for improved Z-height measurement processes which can be rapidly performed and which do not compromise dimensional accuracy.